2:45 PM - 3:00 PM
[SCG54-10] Initial studies of the petrophysics in the dike and upper gabbro from ICDP Hole GT3A, the Oman Drilling Project Phase I
Keywords:ICDP Oman Drilling Project, oceanic crust, physical properties, epidote, D/V Chikyu
Mafic rocks from the Hole GT3A are altered in the various extensions[DAT1] . Compared to the gabbros from the Hole GT1A and GT2A of the Oman Drilling Project, which were described and measured during Leg 1 of ChikyuOman2017 expedition, GT3A cores show much wider range of physical properties. For example, P-wave velocity of the samples from GT3A show a range from 2.2 to 7.1 km/s. There is a clear negative correlation between P-wave velocity and porosity[DAT2] . It is noteworthy that there is a positive correlation between the densities [DAT3] and porosity in more than 1/4 of the samples. Highly altered samples from the GT3A cores show high porosity (up to 12%) and high both bulk and grain densities (up to 3.2 and 3.4 g/cm^3, respectively). It is probably because that the larger volume of epidote with high density (3.39 – 3.48 g/cm^3) in the more altered samples. The color spectrums, especially yellowness of the core samples, clearly have correlations with the rock physics of the GT3A samples (Fig.1). The yellowness of the mafic rocks in the GT3A imply their degree of alteration reflected the mode of epidote. In other words, the epidote precipitation during the hydrothermal alteration reduces the volume of a part of oceanic crust and probably causes the higher porosity as previously proposed on a qualitative basis (Harper et al JGR 1988; Bettison-Varga et al. Geology 1992; Harper GSA Spec Papers 1995; Cann et al., Geofuid 2015).